What’s the worst thing to forget for workout?

I believe one of the worst things to forget is headphones and I found that out the hard way. I’ve forgotten my workout shoes, socks, water, workout shirt, and a towel but I got around those obstacles; when I forgot my shirt I used a jacket as a shirt. It was hot but it was better than using my button up work shirt or going all the way home. Out of all of the things I’ve let at home the worst was the headphones; I couldn’t listen to anything and I thought I could power through it but I was wrong.  I don’t know where my energy went but I really needed it for the treadmill and elliptical; I was tempted when I first walked in the door to wait until the next day to work out but no I was determined. It was horrible and I can say don’t forget the headphones! If I forget my iPod I have my phone to listen to and even if I forget my phone I can listen to the TV’s using the headphone plugs on the machines.

Let us know; what’s the worst thing for you to leave at home when you’re working out?